It has been disclosed in the above-identified applications and patents that certain crystalline layered mixed metal hydroxides can be used in the modification of the viscosity of various fluid formulations. In some of the disclosures, the said mixed metal hydroxides are combined with clay, e.g. bentonite and others, to form adducts which are useful for viscosity modification of drilling fluids and other fluids. In some cases, the viscosity is said to be thixotropic, and in other cases the viscosity is merely said to be thickened or modified. Also, some of the above-identified pending applications disclose that fluids gelled by use of the crystalline layered mixed metal hydroxides will quickly re-gel after being subjected to shear.
In a paper prepared for presentation at the 1990 Drilling Conference of the International Association of Drilling Contractors/Society of Petroleum Engineers in Houston, Tex., Feb. 27-Mar. 2, 1990, the efficacy of using MMH (Mixed Metal Hydroxides) in a drilling mud are disclosed. The papery in its References section on page 5, refers to other papers about the use of MMH in drilling muds at meetings of the IAPC/SPE and SPE Symposium on Oilfield Chemistry in February-Mach 1989. These publications are cumulative to the information disclosed in U.S. Pat. Nos. 4,664,843 and 4,790,954, the publication of which pre-dates these papers.
None of the patents identified above disclose any recognition of an entirely novel type of viscosity effect which is not of the forms previously known, i.e, those known as dilatant, thixotropic, Newtonian, non-Newtonian, psuedo-plastic, Bingham plastic, or rheopexic.
We have now discovered more about these compounds and formulations containing them and have found that stress, rather than shear, produces a reversible phase change from a solid phase to a liquid phase, this is an unrecognized and unexpected phenomenon. In a manner of speaking, it is a phase metamorphosis, not a chemical metamorphosis.
This novel phenomenon is herein given the name of "stress-induced fluidity" as a means of identifying the reversible phase change effect on an elastic solid which readily becomes a relatively low-viscosity fluid under stress. The change from an elastic solid state to a fluid state begins as soon as an applied stress reaches or exceeds a critical strain point and the reversion to an elastic solid is immediate upon ceasing the stress; by "immediate" it is meant that the reversion to the elastic solid state is on the order of about one millisecond or less, essentially too fast for measurement using state of the art measuring devices. It is not the same effect as is obtained using shearing forces to break up a gel or a sol since those do not immediately return to the form of a gel or sol, (such as hydrogel, alcogel, organogel, or electrosol) though some may return to a gel or sol over a detectable period of time. Some of the various previously known forms of gels or sols may even undergo changes under shearing forces which interfere with a complete return to their previous form upon cessation of the shearing forces.
It has now been found that novel elastic solids having stress-induced fluidity are prepared by creating a fluid having distributed therein an effective amount of finely-divided colloids having ionic charge sites and also having distributed therein an effective amount of counter-ionic charge sites, the charge sites being present in a solvent in sufficient quantity to produce an elastic solid having stress-induced fluidity. Preferably, the ionic charge sites are anionic, the counter-ionic charge sites are cationic, and the chemical moieties containing the ionic sites comprise about 0.1 to about 50 percent of the total weight of the elastic solid.
This new discovery is perceived as a reversible phase change of an elastic solid composition having high energy, short range ionic interactions with a very low degree of reinforcement. Because of this a stress-induced fluidization of the elastic solid is reversible, since the high energy, short range interactions are not destroyed, and the low degree of reinforcement permits the fluidization until reversion back to an elastic solid.
These elastic solids having reversible stress-induced fluidity are perceived as being analagous, in their response to a critical strain, to a solid state diode in response to a critical flow of electrons.